The field of the present invention is flow control devices and particularly such devices as are employed with intravenous catheters.
With the advent of sophisticated monitoring equipment, it has become common practice in hospitals and particularly in intensive care facilities to maintain a continuous monitoring of certain body functions. This monitoring often includes intravenous sensing requiring a hollow catheter. The advantages of continuous monitoring of blood pressure and the like using such a hollow catheter have made this practice routine. However, such catheters are subject to blinding by blood clotting over the end in the vein or artery. A relatively successful solution to such blinding has been devised which includes a small medical fluid flow through the catheter. To this end, capillary tubes have been employed. The capillary flow is, however, only a partial solution to the problem. Use of such a system requires a compromise between excessive volumes of flow into the body and insufficient flow to assure against blinding.
To prevent excessive flow into the body and yet provide some means for overcoming clotting, an additional solution has been employed. A manually controlled high volume flow sufficient to insure against blinding of the catheter is used. The high volume flow is also useful for initially filling the catheter line with fluid, for removing air bubbles and the like. Such devices incorporating this bi-flow concept include U.S. Pat. No. 3,675,891 entitled "Continuous Catheter Flushing Apparatus" to Reynolds, et al and U.S. Pat. No. 4,192,303 entitled "Flow Restricting Device for Artificial Catheter Systems" to Young et al. The Reynolds et al and Young et al patents are incorporated herein by reference as indicative of the prior state of the art and to provide further illustration of utility of the present invention.
In overcoming difficulties in durability and convenience of use, a device has been developed which is disclosed in U.S. patent application Ser. No. 312,856, filed Oct. 16, 1981, to Sullivan, entitled "Flow Control Apparatus", the disclosure of which is incorporated herein by reference. The disclosed device includes a resilient block of material with at least one passage therethrough. This block is incorporated in a housing having a hollow body and a plunger. The plunger is also hollow, is slidably positioned in the hollow body and extends therefrom such that by compressing the hollow body and the plunger together, the resilient block is compressed and the passage therein deformed. The passage includes a ball therein which acts as a valve. The deformation of the passage is designed to allow fast flow past the valve.
The Sullivan device was designed to promote deformation of the resilient block solely through compression on the ends thereof. The resulting lateral deformation was generally random as the movement of resilient material around the passage could not be controlled by the operator through simple compression of the device. As particular movement could not be assured, the fit between the valve and the resilient block could not be in substantial interference. However, to insure against valve leakage, some interference fit between the valve and the passage was required. Consequently, a very narrow range of fit between the valve and the resilient block was required in the Sullivan device to gain reasonable reliability. Demanding tolerances and complicated or extensive reliability testing can create production and cost difficulties.